Various methods may be used for controlling the regeneration rate in aftertreatment devices such as diesel particulate filters (DPF) and lean NOx traps (LNT) by metering the oxygen flow through the exhaust aftertreatment system to prevent excessive temperatures which may degrade the aftertreatment devices (see U.S. Pat. No. 6,988,361 and U.S. Pat. No. 7,137,246).
However, the inventors herein have recognized that with such approaches, adjustments in oxygen concentration of one device may cause an undesired exotherm in another device. For example, adjusting the oxygen flow to the DPF during regeneration to manage temperature conditions in the DPF may cause undesired exotherms in a diesel oxidation catalyst (DOC) or a selective catalytic reducing catalyst (SCR) if present in the exhaust aftertreatment system. Alternatively, the inventors herein have recognized that an undesired exotherm may also be caused by various leaks in the engine or exhaust, such as coolant leaks (coolant entering the exhaust and providing reductant), fuel injectors leaks (unintended fuel entering the engine/exhaust system and providing reductants), or a turbo bearing leak.
The inventors herein have recognized the advantage of identifying undesired exotherms in the aftertreatment system during engine operation and initiating mitigating actions in response to the detection of an undesired exotherm. The method may comprise: identifying an undesired exotherm based on an expected oxygen depletion along a length of the exhaust system in a direction of exhaust gas flow of exhaust gas, and; initiating mitigating actions in response to an identified undesired exotherm. For example, the undesired exotherm may be identified based on an expected oxygen concentration taking into account whether a particulate filter region of the exhaust system is regenerating, and if so, to what extent.
In this way, even if filter regeneration can be controlled via adjustments to oxygen concentration in the exhaust, the system is still able to identify if another region of the exhaust system, away from the particulate filter regeneration, is experiencing an undesired exotherm, and thus may be reaching an over-temperature condition. Further, if one or more engine or exhaust components is leaking and causing an undesired exotherm, it is possible to identify the situation even when the oxygen concentration may be controlled to a desired value.
In such an approach, various mitigating actions can be initiated, including reducing fuel rail pressure, adjusting exhaust air-fuel ratio, adjusting injection timing, adjusting torque limit, inducing misfire, modifying urea injection quantity, etc.
As such, it may be possible to address the risk of undesired exotherms occurring from combustible material in the exhaust reacting with excess oxygen due to the primarily lean conditions in exhaust systems, such as diesel systems, when the exhaust is at sufficiently high temperatures, even during controlled particulate filter regeneration operation.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.